Monday, March 23, 2015

Chilled Beams in Healthcare Facilities

HVAC, lighting and additional systems
found in healthcare facilities combine to utilize a vast amount of energy. In
fact, hospitals consume more than 2.5 times the energy in comparison to
average-sized commercial buildings. For this reason, the Department of
Energy and ASHRAE have adopted legislation that calls for a 20% energy
reduction in existing healthcare facilities and a 30% reduction in new
construction.

The reheating of supply air in healthcare facilities has proven inefficient,
due to high-ventilation requirements. This has become a primary target in the
ongoing mission to decrease building energy use. Recently updated guidelines
provide tremendous energy-savings opportunities.

How Do We Save Energy In Healthcare Facilities?

This can be accomplished by implementing active chilled beams in patient rooms
and other areas in which the recirculation of room air is acceptable.
ANSI/ASHRAE Standard 170-2013 Ventilation of Healthcare Facilities establishes
revised regulations for ventilation rates and practices. This standard has also
been adopted by the American Society of Healthcare Engineers (ASHE) as well as the
AIA FGI Guidelines.

Among the revisions are changes in the ventilation requirements for spaces
wherein the recirculation of room air is allowable. They include patient
nursing, diagnostic/treatment and labor/delivery/postpartum rooms. These areas
previously required 6 air-changes-per-hour -- 2 of which were outside air -- of
conditioned and filtered air be delivered to each space.

The amended standard lowers the air-change requirement for these spaces to 4
air changes per hour. It also allows for the recirculation of room air to count
as 2 of those total air changes, provided:

1. Recirculation is limited to the room air itself and does not include any air
from another space.

2. Delivery of a minimum of 2 air
changes of outside air -- filtered through a MERV 14 filter at the AHU -- is
maintained.

The standard also stipulates that no filtering of the recirculated room air is
required, so long as it does not pass over a wetted surface. These updates
clearly promote the use of fan-coil units and chilled beams to reduce reheating
of the supply air.

One of the advantages a beam system possesses over a VAV system is that it
delivers a constant volume (2ACH-1) of 100% outside air at 65°F,
while the VAV system provides all of its sensible cooling by way of its 55°F
primary air supply. This primary air provides 3.6 Btu/h-ft2 of
space sensible cooling; the beam's water-side cooling supplements this to match
the room demand. The coil within the beam removes 16.4 Btu/h-ft2 of
sensible heat to supplement its primary cooling, whereas the VAV system must
deliver 5.5 ACH-1 to meet the 20 Btu/h-ft2 design
load of the space.

VAV systems and beam systems differ in
how they handle periods of reduced demand. A VAV terminal can modulate its
airflow delivery between its minimum airflow rate of 4ACH-1 and
maximum of 5.5 ACH-1; on the other hand, the beam system
throttles its chilled-water flow rate. The latter approach saves energy. If the
space cooling demand drops below 72% of design, the VAV system must begin to
reheat the supply air in order to balance the demand of the space. Additional
reheat is required as space demands drop, increasing energy usage.

That is not the case for a beam setup. The system's minimal primary air
contribution -- 18% of the space sensible design -- allows it to respond to an
82% reduction in space demand, before reheat is required. This, combined with
the fact the air-handling unit is always tasked to deliver less than half as
much air as the VAV system, makes the beam system a hands-down winner!